Electromagnetic actuating means for print hammer

ABSTRACT

An impact printer in which characters moving on an endless chain are struck on-the-fly by print hammers to print the characters on paper. The print hammers are springs supported in flexed conditions by a permanent magnet, and the springs are released by applying an electrical signal to a coil which creates a magnetic field balancing the permanent magnet. Special supports provide different effective lengths for the spring in the cocked and printing positions.

United States Patent Albo et a1.

[54] ELECTROMAGNETIC ACTUATING MEANS FOR PRINT HAMMER [72] Inventors: Ronald T. Albo; John Pastrone, both of I Los Gatos, Calif.

Information Printing Systems Corporation, Santa Clara, Calif.

[22] Filed: Mar. 20, 1970 [21] Appl.N0.: 21,436

[ 73] Assignee:

[52] US. Cl. ..l01/93 C, 317/127, 335/229 [51] Int. Cl [58] Field ofSearch ..l01/93C,93,109,ll1;

[56] References Cited UNITED STATES PATENTS Potter ..l0l/93 C 9/1968 Potter et a1. ..l01/11l X ..-........B4lj 9/38, H01f7/04 [is] 3,656,425 [451 Apr. 18,1972

3,172,352 3/1965 Helms ..10l/93 C 3,156,180 11/1964 Barnes ..l0l/93 C 3,279,362 10/1966 Helms .....101/93 C 3,351,007 11/1967 Poland ..l01/93 C 3,359,921 12/1967 Arnold et al. ..l01/93 C 3,049,990 8/1962 Brown et al ..l01/93 C Primary Examiner-William B. Penn Attorney-Limbach, Limbach & Sutton [5 7] ABSTRACT An impact printer in which characters moving on an endless chain are struck on-the-fly by print hammers to print the characters on paper. The print hammers are springs supported in flexed conditions by a permanent magnet, and the springs are released by applying an electrical signal to a coil which creates a magnetic field balancing the permanent magnet. Special supports provide different effective lengths for the spring in the cocked and printing positions.

4 Claims, 6 Drawing Figures mimwmwwe 3,656,425

SHEET 15F 4 INVENTORS KONAL!) T. M50 JOHN PASTKONE #rg'Em PATENTEDAPR 18 I972 SHEET 2 UF 4 INVENTORS KUNALD I ALSO 'JOHN mama/v5 a 532$ ATTOIUJEYs PATENTEDAPR 18 m2 SHEET 3 [IF 4 INVENTORS I ALSO BY JOHN PASTKOA/E (mm TTOKNEVS RONALO Wa t 5%;,

T"I I PATENTEUAFR 18 I97? 3, 656,425

SHEET '4 OF 4 INVENTORS 20mm mm FIG- -:| BY JOHN. PASTKONE iw rzfiz RELATED APPLICATIONS The paper guidance mechanism in the printer which uses the print hammer of this invention is the subject of an application of John Pastrone and Ingemar I-l. Lundquist, Ser. No. 21,433, filed Mar. 20, 1970 and the print chain used with the hammer of this invention is the subject of an application of John Pastrone, George W. Bowers, Jr., and Tony W. Broski, Jr., Ser. No. 21,464, filed Mar. 20, 1970.

SUMMARY OF INVENTION A variety of printing mechanisms are known including the common typewriter with moving type arms, printers and typewriters with rigid elements which carry multiple characters, and chain printers in which an endless chain of characters are moved between a platen and a set of print hammers. The characters of the chain are struck on-the-fly at proper positions on a print line by operating the hammers at precisely the right times.

Chain printers offer many advantages over other types of printers because the reciprocating parts in a chain printer (the hammers) have minimal inertia, and hence they may be operated very rapidly. A variety of print hammer mechanisms are known having various advantages and disadvantages. One such mechanism is shown in Brown et al US. Pat. No. 3,460,469 where spring hammers are held in a ready position by an electromagnet and released for printing by the magnetic field of an opposing electromagnet. In accordance with this invention, we provide a print hammer mechanism with which many of the advantages of the Brown et al hammer can be obtained while providing substantially improved results.

Thus, we provide a print hammer in which a hammer spring is held in cocked position by a permanent magnet and released by an electrical signal in a balancing coil. We are able to accomplish the use of a permanent magnet by employing a high strength magnet of barium ferrite with specially shaped pole pieces which provide surface area contact with the magnet which is at least three times as great as the cross-sectional area of the gap in the magnetic circuit where the print hammer is held.

The use of the permanent magnet to hold the print hammer in cocked position prevents misprints from occurring at the time the electrical power to the printer is turned off. Additionally, one very inexpensive ceramic magnet may be employed for a large bank of print hammers thereby achieving substantial cost saving over the costs required to hold the hammers electromagnetically.

Improved control over the flight of the hammer after release and recapture by the magnetic field after printing is obtained with mounting fulcrums which provide a longer effective length for the hammer spring during recapture and spring cocking than during printing.

These and other features of the invention will become apparent from the following description of one preferred embodiment of the invention, it being understood that many modifications may be made in the structure disclosed without departing from the spirit and scope of the invention.

DESCRIPTION OF DRAWINGS FIG. 1 is a perspective view of a computer time-share terminal employing the print hammer of this invention;

FIG. 2 is a sectional view through FIG. 1 taken along the plane indicated at 22 in FIG. 1;

FIG. 3 is a central sectional view like FIG. 2 of a fragment of the apparatus shown in FIG. 2 illustrated on a larger scale;

FIG. 4 is an exploded view of the apparatus illustrated in FIG. 3;

FIG. 5 is a top plan view of a bank of the print hammers of FIGS. 3 and 4, and;

FIG. 6 is a face view of the bank of print hammers of FIG. 5 progressively broken away.

DETAILED DESCRIPTION Referring now in detail to FIG. 1, a pedistal 1 containing suitable computer interface electronic equipment supports a case 2 having a conventional typewriter keyboard 4 and platen 6 controlled by platen handles 8. A conventional paper holddown arm 10 is mounted above the platen, and the platen is provided with an adjustment lever 12 by which paper thickness may be adjusted and a release lever 14 which may be operated to release pinch rollers 16 and 18 (FIG. 2) holding typewriter paper in engagement with platen 6. Lever 14 may also be employed to move platen 6 away from paper guide 34 (FIG. 2) to facilitate introduction of computer forms 32 along path 26 through guides 28 and 30 past a frictional guide spring 34 to a tractor drive 40.

Adjacent to the path of paper on either path 24 or 26 near platen 6 a print character chain 22 is moved past a bank of print hammers 25. The chain 22 carries individual characters 42 (FIG. 6) which, when struck by a hammer 25 impress a character on paper on the platen. As seen in FIG. 3, a typewriter ribbon 44 is supported between the characters 42 and the platen 6 to provide an inked impression of the character when struck, and preferably the typewriter ribbon 44 is reciprocated up and down so that at any time when the ribbon need not be present to provide an impression, the line of type previously typed by the operator is visible for inspection.

With reference to FIGS. 3 and 4, the print hammer apparatus of this invention includes a base plate 46 made of a material having a very low magnetic permeability. Supported above the base plate 46 is an elongated ceramic magnet 48 made of a strong magnetic material such as barium ferrite with forward and rearward pole pieces 50 and 52 supported against opposite faces of the magnet 48 by screws 54. The rearward pole piece carries an arm portion 56 mounted on the rear pole piece 52 by a pair of adjusting screws 58 received in an elongated slot 60, and a wire wound coil 62 is wound on the arm portion 56.

The forward pole piece 50 is provided with a plurality of upstanding ears 64 separated by slots 66, and it will be apparent from inspection of FIG. 5, that the arm portions 56 of rearward pole pieces 52 are aligned with the slots 66 between the ear 64 on the forward pole piece thereby providing a substantially closed magnetic path illustrated by the dotted line 68 in FIG. 4 having a gap illustrated symbolically at 70 in FIG. 4 between the arm 56 of the rear pole piece and the cars 64 of the forward pole piece. As explained hereinafter, this gap 70 provides an area of high intensity magnetic field into which a magnetically permeable part of a movable hammer member is held in a print ready position. In order to provide efficient capture and holding of the movable print hammer member, the cross-sectional area of the gap 70 is less than about one-third of the surface area of each of the forward and rearward pole pieces (illustrated at 72 in FIG. 4) where those pole pieces engage the surface of the permanent magnet. With this relation observed, magnetic saturation is achieved in the magnetically permeable part of the movable print hammer where that part moves into the gap 70 in the hammer cocked condition.

A print hammer 25 is mounted on the forward pole piece 50 aligned with each of the slots 66, and the print hammer 25 includes a flat leaf spring portion 74 with an integral curved neck 76 terminating in a forward anvil 78 integrally formed with the spring. A blade 80 made of a material different from the spring 74 and having a high magnetic permeability is rigidly attached to the flat spring portion 74, and the entire hammer is rigidly mounted on the forward pole piece 50 by a pair of screws 82.

As explained above, the effective length of the spring hammer 25 is controlled by special mounting means which includes a first mounting portion 84 and a second mounting portion 86. Each of the mounting portions 84 and 86 is illustrated as a separate piece individually mounted on each of the spring hammers 25, but all of the mounting portions 86 for all of the hammers 25 may constitute a single piece, and all of the mounting portions 84 for all the hammers may constitute a single piece or a single projection on the forward face of the forward pole piece 50.

As illustrated in FIGS. 3 and 4, the mounting portion 84 is sandwiched between the forward pole piece 50 and flat spring 74 with its upper end positioned at a predetermined distance below the top free end of the spring hammer 25. The outer mounting portion 86 is rigidly held against the face of the spring 74 by screws 82 and has its upper end located at 74 substantially above the upper end of the mounting portion 84 so that the spring hammer 25 has an effective spring length at the time of capture and holding in the cocked position which is substantially longer than the effective length of the spring when the hammer 25 reaches its forward released printing position. The upper ends of the mounting portions 84 and 86 function as fulcrums on the spring, but these upper ends are slightly rounded as illustrated in FIG. 3 to prevent excessive fatigue of the springs.

We claim:

1. A print hammer assembly for a chain printer comprising:

A. a permanent magnet;

B. first and second pole pieces made of magnetically permeable material attached to said permanent magnet at opposite poles thereof with said pole pieces and said permanent magnet defining a substantially closed magnetic path having a gap therein;

C. one of said pole pieces having an arm portion thereon cooperating with means on said other pole piece through which said magnetic path passes;

D. a leaf spring having a fixed end and a movable end with said spring mounted adjacent to said pole pieces so that said movable end thereof is movable toward and away from said arm portion;

E. a blade made of magnetically permeable material on said spring near the movable end thereof with said blade mounted on the side of said spring near said arm portion whereby said spring is held in flexed position and said blade is held in said gap in close juxtaposition to said arm portion;

F. an electrical coil wrapped around said arm portion of said pole piece whereby an electrical current in said coil creates a magnetic field in said path opposing said permanent magnet so that said blade is adapted to be released and the blade moved away from said arm portion as said spring unflexes; and,

G. an anvil portion on the free end of said spring adapted to strike a printing blow when said blade is released and said spring unfiexes.

2. The print hammer of claim 1 characterized further by the inclusion of mounting means for said spring which comprises:

a first mounting portion engaging the side of said spring near said pole pieces with said first mounting portion engaging said spring at a predetermined distance from the movable end thereof, and;

a second mounting portion engaging the side of said spring opposite to said pole pieces with said second mounting portion engaging said spring at a position along its length between the free end thereof and said first mounting portion;

whereby the effective length of said spring is greater when said spring is held by said magnetic path than when said anvil portion strikes a printing blow.

3. The print hammer of claim 1 characterized further in that said leaf spring has a flat body portion and an integral neck at the movable end of the spring extending generally perpendicular to said body portion with said anvil portion integrally formed with said body and neck portions, and said blade is made of a piece separate from said spring and rigidly attached to said flat body portion on the opposite side thereof from said neck.

4. The apparatus of claim 1 characterized further in that each of said pole pieces has a surface area in contact with said permanent magnet which is at least three times as great as the cross-sectional area of said gap. 

1. A print hammer assembly for a chain printer comprising: A. a permanent magnet; B. first and second pole pieces made of magnetically permeable material attached to said permanent magnet at opposite poles thereof with said pole pieces and said permanent magnet defining a substantially closed magnetic path having a gap therein; C. one of said pole pieces having an arm portion thereon cooperating with means on said other pole piece through which said magnetic path passes; D. a leaf spring having a fixed end and a movable end with said spring mounted adjacent to said pole pieces so that said movable end thereof is movable toward and away from said arm portion; E. a blade made of magnetically permeable material on said spring near the movable end thereof with said blade mounted on the side of said spring near said arm portion whereby said spring is held in flexed position and said blade is held in said gap in close juxtaposition to said arm portion; F. an electrical coil wrapped around said arm portion of said pole piece whereby an electrical current in said coil creates a magnetic field in said path opposing said permanent magnet so that said blade is adapted to be released and the blade moved away from said arm portion as said spring unflexes; and, G. an anvil portion on the free end of said spring adapted to strike a printing blow when said blade is released and said spring unflexes.
 2. The print hammer of claim 1 characterized further by the inclusion of mounting means for said spring which comprises: a first mounting portion engaging the side of said spring near said pole pieces with said first mounting portion engaging said spring at a predetermined distance from the movable end thereof, aNd; a second mounting portion engaging the side of said spring opposite to said pole pieces with said second mounting portion engaging said spring at a position along its length between the free end thereof and said first mounting portion; whereby the effective length of said spring is greater when said spring is held by said magnetic path than when said anvil portion strikes a printing blow.
 3. The print hammer of claim 1 characterized further in that said leaf spring has a flat body portion and an integral neck at the movable end of the spring extending generally perpendicular to said body portion with said anvil portion integrally formed with said body and neck portions, and said blade is made of a piece separate from said spring and rigidly attached to said flat body portion on the opposite side thereof from said neck.
 4. The apparatus of claim 1 characterized further in that each of said pole pieces has a surface area in contact with said permanent magnet which is at least three times as great as the cross-sectional area of said gap. 